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| author |  Uros Bizjak <ubizjak@gmail.com>
| 2022-07-14 19:16:53 +0200 |
|---|---|---|
| committer |  Andrew Morton <akpm@linux-foundation.org>
| 2022-09-11 21:55:07 -0700 |
| commit | b0192296b45232872720d969366449c001ab1f4a (patch) | |
| tree | e4c722c8935747ded01af079f6e1c8302264c2b5 /fs/buffer.c | |
| parent | epoll: use try_cmpxchg in list_add_tail_lockless (diff) | |
| download | linux-b0192296b45232872720d969366449c001ab1f4a.tar.gz linux-b0192296b45232872720d969366449c001ab1f4a.tar.bz2 linux-b0192296b45232872720d969366449c001ab1f4a.zip | |
buffer: use try_cmpxchg in discard_buffer
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
discard_buffer. x86 CMPXCHG instruction returns success in ZF flag, so
this change saves a compare after cmpxchg (and related move instruction in
front of cmpxchg).
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails, enabling further code simplifications.
Note that the value from *ptr should be read using READ_ONCE to prevent
the compiler from merging, refetching or reordering the read.
No functional change intended.
Link: https://lkml.kernel.org/r/20220714171653.12128-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'fs/buffer.c')
| -rw-r--r-- | fs/buffer.c | 14 |
1 files changed, 5 insertions, 9 deletions
diff --git a/fs/buffer.c b/fs/buffer.c index 55e762a58eb6..2fd98bb7d74e 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -1464,19 +1464,15 @@ EXPORT_SYMBOL(set_bh_page); static void discard_buffer(struct buffer_head * bh) { - unsigned long b_state, b_state_old; + unsigned long b_state; lock_buffer(bh); clear_buffer_dirty(bh); bh->b_bdev = NULL; - b_state = bh->b_state; - for (;;) { - b_state_old = cmpxchg(&bh->b_state, b_state, - (b_state & ~BUFFER_FLAGS_DISCARD)); - if (b_state_old == b_state) - break; - b_state = b_state_old; - } + b_state = READ_ONCE(bh->b_state); + do { + } while (!try_cmpxchg(&bh->b_state, &b_state, + b_state & ~BUFFER_FLAGS_DISCARD)); unlock_buffer(bh); } |